This invention relates generally to the art of automatic screw machines, and more specifically concerns a retrofit apparatus which converts existing conventional single spindle automatic screw machines to numerically controlled machines.
Conventional automatic screw machines have been known and used in the art for some time. The operational functions necessary to produce a given article are accomplished in an automatic, prescribed sequence by the machine. Such machines have a high capability for producing a large number of identical parts fairly rapidly. Automatic screw machines are particularly useful when large quantities of a single machined article are required. They lose their advantage, however, when smaller quantities are required, because of the time and expense necessary to produce the special control cams.
One of the operational functions of the automatically controlled machine is the movement of the machine tool relative to the work piece, which is generally accomplished by longitudinal movement of a turret and lateral movement of two or more cross slides. At least two cross slides are usually provided on a conventional screw machine. The two basic cross slides move laterally relative to the machine, and in the same horizontal plane as the movement of the turret. Additional cross slides may also be present, which slides are in the same vertical plane as the basic cross slides but are positioned at specified angles relative to the basic cross slides.
Other operational functions important to the performance of the machine include the indexing of the turret, the feedout of the stock, and the control of the spindle speeds. In addition, special purpose operational functions, like a deep hole drilling apparatus, may be provided on the machine.
In conventional automatic screw machines, the timed sequence of the above functions are controlled mechanically through cams, trip drums, trip levers and cam followers, which result in the engagement of the conventional machine mechanisms through clutches, gears, etc. at the proper time. Such an arrangement of mechanical devices is found in any conventional automatic screw machine.
The use of trip drum/cam/camshaft arrangement as a timing device has significant limitations, however, both in the time required to turn one article, and the time and expense required to produce the cams. A set of cams made for one job can be used on other jobs, although any change in machine speed or feedrate in any part of the sequence will result in slowing down the entire job. The alternative is to make a complete new set of cams specifically designed for the job.
Valuable time is also lost in the manufacturing sequence itself with the cams, as the tools shift position in the operation sequence. The tools chatter if the changes made in the sequence are too abrupt when a cam controls the timing. Thus, a certain amount of time in the manufacture of each article is lost because custom made cams are used as the timing control. In addition, each new article to be manufactured, or "job", usually requires several new cams. The manufacture of these cams require significant time and expense. If cams from another job can be used, they are usually not optimum, thus causing a further waste in time.
Hence, it is desirable that the operational sequence of the automatic screw machine be controlled by a numerical control apparatus. With numerical control apparatus, the machine functions can be controlled through electrical signals by a program, and the requirements of each job can be programmed into the apparatus easily and quickly. New automatic screw machines have been developed which have this numerical control capability. However, there is no known method or apparatus for retrofitting existing conventional automatic screw machines to permit numerical control of the timing functions.
Accordingly, it is a general object of the present invention to provide a method and apparatus for converting a conventional automatic screw machine to numerical control which overcomes one or more of the disadvantages of the prior art discussed above.
It is another object of the present invention to provide such a method and apparatus which electrically controls the timing of the various conventional automatic screw machine functions.
It is an additional object of the present invention to provide such a method and apparatus which is designed to adapt existing automatic screw machines to electrical timing control.
It is a further object of the present invention to provide such a method and apparatus which will decrease the time necessary for a conventional screw machine to produce a particular article.
It is yet another object of the present invention to provide such a method and apparatus which will simplify the process of setting the screw machine to produce a given article.